- java.lang.Object
-
- java.text.Format
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- java.text.MessageFormat
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- All Implemented Interfaces:
- Serializable, Cloneable
public class MessageFormat extends Format
MessageFormat
provides a means to produce concatenated messages in a language-neutral way. Use this to construct messages displayed for end users.MessageFormat
takes a set of objects, formats them, then inserts the formatted strings into the pattern at the appropriate places.Note:
MessageFormat
differs from the otherFormat
classes in that you create aMessageFormat
object with one of its constructors (not with agetInstance
style factory method). The factory methods aren't necessary becauseMessageFormat
itself doesn't implement locale specific behavior. Any locale specific behavior is defined by the pattern that you provide as well as the subformats used for inserted arguments.Patterns and Their Interpretation
MessageFormat
uses patterns of the following form:MessageFormatPattern: String MessageFormatPattern FormatElement String FormatElement: { ArgumentIndex } { ArgumentIndex , FormatType } { ArgumentIndex , FormatType , FormatStyle } FormatType: one of number date time choice FormatStyle: short medium long full integer currency percent SubformatPattern
Within a String, a pair of single quotes can be used to quote any arbitrary characters except single quotes. For example, pattern string
"'{0}'"
represents string"{0}"
, not a FormatElement. A single quote itself must be represented by doubled single quotes''
throughout a String. For example, pattern string"'{''}'"
is interpreted as a sequence of'{
(start of quoting and a left curly brace),''
(a single quote), and}'
(a right curly brace and end of quoting), not'{'
and'}'
(quoted left and right curly braces): representing string"{'}"
, not"{}"
.A SubformatPattern is interpreted by its corresponding subformat, and subformat-dependent pattern rules apply. For example, pattern string
"{1,number,$'#',##}"
(SubformatPattern with underline) will produce a number format with the pound-sign quoted, with a result such as:"$#31,45"
. Refer to eachFormat
subclass documentation for details.Any unmatched quote is treated as closed at the end of the given pattern. For example, pattern string
"'{0}"
is treated as pattern"'{0}'"
.Any curly braces within an unquoted pattern must be balanced. For example,
"ab {0} de"
and"ab '}' de"
are valid patterns, but"ab {0'}' de"
,"ab } de"
and"''{''"
are not.- Warning:
- The rules for using quotes within message
format patterns unfortunately have shown to be somewhat confusing.
In particular, it isn't always obvious to localizers whether single
quotes need to be doubled or not. Make sure to inform localizers about
the rules, and tell them (for example, by using comments in resource
bundle source files) which strings will be processed by
MessageFormat
. Note that localizers may need to use single quotes in translated strings where the original version doesn't have them.
The ArgumentIndex value is a non-negative integer written using the digits
'0'
through'9'
, and represents an index into thearguments
array passed to theformat
methods or the result array returned by theparse
methods.The FormatType and FormatStyle values are used to create a
Format
instance for the format element. The following table shows how the values map toFormat
instances. Combinations not shown in the table are illegal. A SubformatPattern must be a valid pattern string for theFormat
subclass used.Usage Information
Here are some examples of usage. In real internationalized programs, the message format pattern and other static strings will, of course, be obtained from resource bundles. Other parameters will be dynamically determined at runtime.
The first example uses the static method
MessageFormat.format
, which internally creates aMessageFormat
for one-time use:
The output is:int planet = 7; String event = "a disturbance in the Force"; String result = MessageFormat.format( "At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.", planet, new Date(), event);
At 12:30 PM on Jul 3, 2053, there was a disturbance in the Force on planet 7.
The following example creates a
MessageFormat
instance that can be used repeatedly:
The output with different values forint fileCount = 1273; String diskName = "MyDisk"; Object[] testArgs = {new Long(fileCount), diskName}; MessageFormat form = new MessageFormat( "The disk \"{1}\" contains {0} file(s)."); System.out.println(form.format(testArgs));
fileCount
:The disk "MyDisk" contains 0 file(s). The disk "MyDisk" contains 1 file(s). The disk "MyDisk" contains 1,273 file(s).
For more sophisticated patterns, you can use a
ChoiceFormat
to produce correct forms for singular and plural:
The output with different values forMessageFormat form = new MessageFormat("The disk \"{1}\" contains {0}."); double[] filelimits = {0,1,2}; String[] filepart = {"no files","one file","{0,number} files"}; ChoiceFormat fileform = new ChoiceFormat(filelimits, filepart); form.setFormatByArgumentIndex(0, fileform); int fileCount = 1273; String diskName = "MyDisk"; Object[] testArgs = {new Long(fileCount), diskName}; System.out.println(form.format(testArgs));
fileCount
:The disk "MyDisk" contains no files. The disk "MyDisk" contains one file. The disk "MyDisk" contains 1,273 files.
You can create the
ChoiceFormat
programmatically, as in the above example, or by using a pattern. SeeChoiceFormat
for more information.form.applyPattern( "There {0,choice,0#are no files|1#is one file|1<are {0,number,integer} files}.");
Note: As we see above, the string produced by a
ChoiceFormat
inMessageFormat
is treated as special; occurrences of '{' are used to indicate subformats, and cause recursion. If you create both aMessageFormat
andChoiceFormat
programmatically (instead of using the string patterns), then be careful not to produce a format that recurses on itself, which will cause an infinite loop.When a single argument is parsed more than once in the string, the last match will be the final result of the parsing. For example,
MessageFormat mf = new MessageFormat("{0,number,#.##}, {0,number,#.#}"); Object[] objs = {new Double(3.1415)}; String result = mf.format( objs ); // result now equals "3.14, 3.1" objs = null; objs = mf.parse(result, new ParsePosition(0)); // objs now equals {new Double(3.1)}
Likewise, parsing with a
MessageFormat
object using patterns containing multiple occurrences of the same argument would return the last match. For example,MessageFormat mf = new MessageFormat("{0}, {0}, {0}"); String forParsing = "x, y, z"; Object[] objs = mf.parse(forParsing, new ParsePosition(0)); // result now equals {new String("z")}
Synchronization
Message formats are not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.
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Nested Class Summary
Nested Classes Modifier and Type Class and Description static class
MessageFormat.Field
Defines constants that are used as attribute keys in theAttributedCharacterIterator
returned fromMessageFormat.formatToCharacterIterator
.
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Constructor Summary
Constructors Constructor and Description MessageFormat(String pattern)
Constructs a MessageFormat for the default locale and the specified pattern.MessageFormat(String pattern, Locale locale)
Constructs a MessageFormat for the specified locale and pattern.
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Method Summary
Methods Modifier and Type Method and Description void
applyPattern(String pattern)
Sets the pattern used by this message format.Object
clone()
Creates and returns a copy of this object.boolean
equals(Object obj)
Equality comparison between two message format objectsStringBuffer
format(Object[] arguments, StringBuffer result, FieldPosition pos)
Formats an array of objects and appends theMessageFormat
's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer
.StringBuffer
format(Object arguments, StringBuffer result, FieldPosition pos)
Formats an array of objects and appends theMessageFormat
's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer
.static String
format(String pattern, Object... arguments)
Creates a MessageFormat with the given pattern and uses it to format the given arguments.AttributedCharacterIterator
formatToCharacterIterator(Object arguments)
Formats an array of objects and inserts them into theMessageFormat
's pattern, producing anAttributedCharacterIterator
.Format[]
getFormats()
Gets the formats used for the format elements in the previously set pattern string.Format[]
getFormatsByArgumentIndex()
Gets the formats used for the values passed intoformat
methods or returned fromparse
methods.Locale
getLocale()
Gets the locale that's used when creating or comparing subformats.int
hashCode()
Generates a hash code for the message format object.Object[]
parse(String source)
Parses text from the beginning of the given string to produce an object array.Object[]
parse(String source, ParsePosition pos)
Parses the string.Object
parseObject(String source, ParsePosition pos)
Parses text from a string to produce an object array.void
setFormat(int formatElementIndex, Format newFormat)
Sets the format to use for the format element with the given format element index within the previously set pattern string.void
setFormatByArgumentIndex(int argumentIndex, Format newFormat)
Sets the format to use for the format elements within the previously set pattern string that use the given argument index.void
setFormats(Format[] newFormats)
Sets the formats to use for the format elements in the previously set pattern string.void
setFormatsByArgumentIndex(Format[] newFormats)
Sets the formats to use for the values passed intoformat
methods or returned fromparse
methods.void
setLocale(Locale locale)
Sets the locale to be used when creating or comparing subformats.String
toPattern()
Returns a pattern representing the current state of the message format.-
Methods inherited from class java.text.Format
format, parseObject
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Constructor Detail
-
MessageFormat
public MessageFormat(String pattern)
Constructs a MessageFormat for the default locale and the specified pattern. The constructor first sets the locale, then parses the pattern and creates a list of subformats for the format elements contained in it. Patterns and their interpretation are specified in the class description.- Parameters:
pattern
- the pattern for this message format- Throws:
IllegalArgumentException
- if the pattern is invalid
-
MessageFormat
public MessageFormat(String pattern, Locale locale)
Constructs a MessageFormat for the specified locale and pattern. The constructor first sets the locale, then parses the pattern and creates a list of subformats for the format elements contained in it. Patterns and their interpretation are specified in the class description.- Parameters:
pattern
- the pattern for this message formatlocale
- the locale for this message format- Throws:
IllegalArgumentException
- if the pattern is invalid- Since:
- 1.4
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Method Detail
-
setLocale
public void setLocale(Locale locale)
Sets the locale to be used when creating or comparing subformats. This affects subsequent calls- to the
applyPattern
andtoPattern
methods if format elements specify a format type and therefore have the subformats created in theapplyPattern
method, as well as - to the
format
andformatToCharacterIterator
methods if format elements do not specify a format type and therefore have the subformats created in the formatting methods.
- Parameters:
locale
- the locale to be used when creating or comparing subformats
- to the
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getLocale
public Locale getLocale()
Gets the locale that's used when creating or comparing subformats.- Returns:
- the locale used when creating or comparing subformats
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applyPattern
public void applyPattern(String pattern)
Sets the pattern used by this message format. The method parses the pattern and creates a list of subformats for the format elements contained in it. Patterns and their interpretation are specified in the class description.- Parameters:
pattern
- the pattern for this message format- Throws:
IllegalArgumentException
- if the pattern is invalid
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toPattern
public String toPattern()
Returns a pattern representing the current state of the message format. The string is constructed from internal information and therefore does not necessarily equal the previously applied pattern.- Returns:
- a pattern representing the current state of the message format
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setFormatsByArgumentIndex
public void setFormatsByArgumentIndex(Format[] newFormats)
Sets the formats to use for the values passed intoformat
methods or returned fromparse
methods. The indices of elements innewFormats
correspond to the argument indices used in the previously set pattern string. The order of formats innewFormats
thus corresponds to the order of elements in thearguments
array passed to theformat
methods or the result array returned by theparse
methods.If an argument index is used for more than one format element in the pattern string, then the corresponding new format is used for all such format elements. If an argument index is not used for any format element in the pattern string, then the corresponding new format is ignored. If fewer formats are provided than needed, then only the formats for argument indices less than
newFormats.length
are replaced.- Parameters:
newFormats
- the new formats to use- Throws:
NullPointerException
- ifnewFormats
is null- Since:
- 1.4
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setFormats
public void setFormats(Format[] newFormats)
Sets the formats to use for the format elements in the previously set pattern string. The order of formats innewFormats
corresponds to the order of format elements in the pattern string.If more formats are provided than needed by the pattern string, the remaining ones are ignored. If fewer formats are provided than needed, then only the first
newFormats.length
formats are replaced.Since the order of format elements in a pattern string often changes during localization, it is generally better to use the
setFormatsByArgumentIndex
method, which assumes an order of formats corresponding to the order of elements in thearguments
array passed to theformat
methods or the result array returned by theparse
methods.- Parameters:
newFormats
- the new formats to use- Throws:
NullPointerException
- ifnewFormats
is null
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setFormatByArgumentIndex
public void setFormatByArgumentIndex(int argumentIndex, Format newFormat)
Sets the format to use for the format elements within the previously set pattern string that use the given argument index. The argument index is part of the format element definition and represents an index into thearguments
array passed to theformat
methods or the result array returned by theparse
methods.If the argument index is used for more than one format element in the pattern string, then the new format is used for all such format elements. If the argument index is not used for any format element in the pattern string, then the new format is ignored.
- Parameters:
argumentIndex
- the argument index for which to use the new formatnewFormat
- the new format to use- Since:
- 1.4
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setFormat
public void setFormat(int formatElementIndex, Format newFormat)
Sets the format to use for the format element with the given format element index within the previously set pattern string. The format element index is the zero-based number of the format element counting from the start of the pattern string.Since the order of format elements in a pattern string often changes during localization, it is generally better to use the
setFormatByArgumentIndex
method, which accesses format elements based on the argument index they specify.- Parameters:
formatElementIndex
- the index of a format element within the patternnewFormat
- the format to use for the specified format element- Throws:
ArrayIndexOutOfBoundsException
- ifformatElementIndex
is equal to or larger than the number of format elements in the pattern string
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getFormatsByArgumentIndex
public Format[] getFormatsByArgumentIndex()
Gets the formats used for the values passed intoformat
methods or returned fromparse
methods. The indices of elements in the returned array correspond to the argument indices used in the previously set pattern string. The order of formats in the returned array thus corresponds to the order of elements in thearguments
array passed to theformat
methods or the result array returned by theparse
methods.If an argument index is used for more than one format element in the pattern string, then the format used for the last such format element is returned in the array. If an argument index is not used for any format element in the pattern string, then null is returned in the array.
- Returns:
- the formats used for the arguments within the pattern
- Since:
- 1.4
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getFormats
public Format[] getFormats()
Gets the formats used for the format elements in the previously set pattern string. The order of formats in the returned array corresponds to the order of format elements in the pattern string.Since the order of format elements in a pattern string often changes during localization, it's generally better to use the
getFormatsByArgumentIndex
method, which assumes an order of formats corresponding to the order of elements in thearguments
array passed to theformat
methods or the result array returned by theparse
methods.- Returns:
- the formats used for the format elements in the pattern
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format
public final StringBuffer format(Object[] arguments, StringBuffer result, FieldPosition pos)
Formats an array of objects and appends theMessageFormat
's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer
.The text substituted for the individual format elements is derived from the current subformat of the format element and the
arguments
element at the format element's argument index as indicated by the first matching line of the following table. An argument is unavailable ifarguments
isnull
or has fewer than argumentIndex+1 elements.Subformat Argument Formatted Text any unavailable "{" + argumentIndex + "}"
any null
"null"
instanceof ChoiceFormat
any subformat.format(argument).indexOf('{') >= 0 ?
(new MessageFormat(subformat.format(argument), getLocale())).format(argument) : subformat.format(argument)!= null
any subformat.format(argument)
null
instanceof Number
NumberFormat.getInstance(getLocale()).format(argument)
null
instanceof Date
DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)
null
instanceof String
argument
null
any argument.toString()
If
pos
is non-null, and refers toField.ARGUMENT
, the location of the first formatted string will be returned.- Parameters:
arguments
- an array of objects to be formatted and substituted.result
- where text is appended.pos
- On input: an alignment field, if desired. On output: the offsets of the alignment field.- Throws:
IllegalArgumentException
- if an argument in thearguments
array is not of the type expected by the format element(s) that use it.
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format
public static String format(String pattern, Object... arguments)
Creates a MessageFormat with the given pattern and uses it to format the given arguments. This is equivalent to(new
MessageFormat
(pattern)).format
(arguments, new StringBuffer(), null).toString()- Throws:
IllegalArgumentException
- if the pattern is invalid, or if an argument in thearguments
array is not of the type expected by the format element(s) that use it.
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format
public final StringBuffer format(Object arguments, StringBuffer result, FieldPosition pos)
Formats an array of objects and appends theMessageFormat
's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer
. This is equivalent toformat
((Object[]) arguments, result, pos)- Specified by:
format
in classFormat
- Parameters:
arguments
- an array of objects to be formatted and substituted.result
- where text is appended.pos
- On input: an alignment field, if desired. On output: the offsets of the alignment field.- Returns:
- the string buffer passed in as
toAppendTo
, with formatted text appended - Throws:
IllegalArgumentException
- if an argument in thearguments
array is not of the type expected by the format element(s) that use it.
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formatToCharacterIterator
public AttributedCharacterIterator formatToCharacterIterator(Object arguments)
Formats an array of objects and inserts them into theMessageFormat
's pattern, producing anAttributedCharacterIterator
. You can use the returnedAttributedCharacterIterator
to build the resulting String, as well as to determine information about the resulting String.The text of the returned
AttributedCharacterIterator
is the same that would be returned byformat
(arguments, new StringBuffer(), null).toString()In addition, the
AttributedCharacterIterator
contains at least attributes indicating where text was generated from an argument in thearguments
array. The keys of these attributes are of typeMessageFormat.Field
, their values areInteger
objects indicating the index in thearguments
array of the argument from which the text was generated.The attributes/value from the underlying
Format
instances thatMessageFormat
uses will also be placed in the resultingAttributedCharacterIterator
. This allows you to not only find where an argument is placed in the resulting String, but also which fields it contains in turn.- Overrides:
formatToCharacterIterator
in classFormat
- Parameters:
arguments
- an array of objects to be formatted and substituted.- Returns:
- AttributedCharacterIterator describing the formatted value.
- Throws:
NullPointerException
- ifarguments
is null.IllegalArgumentException
- if an argument in thearguments
array is not of the type expected by the format element(s) that use it.- Since:
- 1.4
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parse
public Object[] parse(String source, ParsePosition pos)
Parses the string.Caveats: The parse may fail in a number of circumstances. For example:
- If one of the arguments does not occur in the pattern.
- If the format of an argument loses information, such as with a choice format where a large number formats to "many".
- Does not yet handle recursion (where the substituted strings contain {n} references.)
- Will not always find a match (or the correct match) if some part of the parse is ambiguous. For example, if the pattern "{1},{2}" is used with the string arguments {"a,b", "c"}, it will format as "a,b,c". When the result is parsed, it will return {"a", "b,c"}.
- If a single argument is parsed more than once in the string, then the later parse wins.
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parse
public Object[] parse(String source) throws ParseException
Parses text from the beginning of the given string to produce an object array. The method may not use the entire text of the given string.See the
parse(String, ParsePosition)
method for more information on message parsing.- Parameters:
source
- AString
whose beginning should be parsed.- Returns:
- An
Object
array parsed from the string. - Throws:
ParseException
- if the beginning of the specified string cannot be parsed.
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parseObject
public Object parseObject(String source, ParsePosition pos)
Parses text from a string to produce an object array.The method attempts to parse text starting at the index given by
pos
. If parsing succeeds, then the index ofpos
is updated to the index after the last character used (parsing does not necessarily use all characters up to the end of the string), and the parsed object array is returned. The updatedpos
can be used to indicate the starting point for the next call to this method. If an error occurs, then the index ofpos
is not changed, the error index ofpos
is set to the index of the character where the error occurred, and null is returned.See the
parse(String, ParsePosition)
method for more information on message parsing.- Specified by:
parseObject
in classFormat
- Parameters:
source
- AString
, part of which should be parsed.pos
- AParsePosition
object with index and error index information as described above.- Returns:
- An
Object
array parsed from the string. In case of error, returns null. - Throws:
NullPointerException
- ifpos
is null.
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clone
public Object clone()
Creates and returns a copy of this object.
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equals
public boolean equals(Object obj)
Equality comparison between two message format objects- Overrides:
equals
in classObject
- Parameters:
obj
- the reference object with which to compare.- Returns:
true
if this object is the same as the obj argument;false
otherwise.- See Also:
Object.hashCode()
,HashMap
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hashCode
public int hashCode()
Generates a hash code for the message format object.- Overrides:
hashCode
in classObject
- Returns:
- a hash code value for this object.
- See Also:
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
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Dokument erstellt 11/06/2005, zuletzt geändert 04/03/2020
Quelle des gedruckten Dokuments:https://www.gaudry.be/de/java-api-rf-java/text/messageformat.html
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